The rapid development of digital technology has created new opportunities for the education sector by facilitating its integration into the teaching and learning process (Razak et al., 2022). While digital learning is already well-known, its adoption in education continues to grow and expand globally ((Amin & Sundari, 2020); (Islam Sarker et al., 2019)). This trend underscores the critical role of digital learning in enhancing the educational experience for both teachers and students.

In Indonesia, the digital transformation of education has posed significant challenges, particularly with the adoption of modern digital learning technologies and tools following the COVID-19 pandemic (Kovalenko et al., 2022). Educational practices incorporating digital resources are increasingly being developed across all educational levels, though implementation remains uneven (Cabero-Almenara et al., 2022). Despite these advances, educational innovation still faces several challenges, including technological development, resource availability, pedagogical adjustments, and—most importantly—teacher preparedness to adopt new teaching methods (Lavicza et al., 2022). Recognizing these challenges, Indonesia's Ministry of Education and Culture launched the School Digitalization Program to provide technological tools and professional training for teachers and students across various regions (Kebudayaan, 2022).

Twenty-first-century skills encompass the ability to create, use, critically evaluate, and contextualize information from various sources. Integrating real-world contexts into a virtual learning environment requires advanced technologies that can simulate real-world scenarios (Maas & Hughes, 2020). In today’s digital era, books have evolved from traditional printed formats to digital forms, offering greater practicality and convenience. Digital books, being portable and easily accessible, enable readers to study anytime and anywhere without needing to navigate entire texts manually ((Nurhayati, 2017); (Awang, 2010)). Digital books serve as interactive learning media that provide virtual experiences (Cordón-García et al., 2016). Research by Park et al. (2019) highlights how adopting digital books can increase student motivation and engagement. Consequently, teachers often integrate digital books into their lessons to create a dynamic and conducive learning environment (Lovenburg, 2018). Moreover, (Hull & Chaparro, 2006) demonstrated that digital books could offer interactive three-dimensional content, enhancing user engagement and comprehension. In alignment with these developments, the Indonesian National Core Curriculum has begun incorporating digital technology to make learning more relevant and adaptable to technological advancements (Kebudayaan, 2024).

Digital books become more engaging when they integrate real-world environments into virtual spaces, enabling users to interact through a seamless blend of physical and digital elements. A key technology that supports this integration is Mixed Reality (MR), which presents digital objects within the real world while allowing users to interact with them through touch and gestures. Although MR is emerging as a promising educational tool, its application in schools remains limited (Gattullo et al., 2022). Mixed Reality plays an increasingly important role in education by promoting active participation and knowledge development within a safe and engaging learning environment (Ogunseiju et al., 2022). It merges the real and virtual worlds, providing contextual learning experiences that allow students to explore realistic environments enriched with virtual interactions (Kaplan et al., 2021). Research has demonstrated that MR enhances material comprehension, language learning, and motivation for academic performance ((Bacca et al., 2014); (Lindgren & Johnson-Glenberg, 2013); (Radu, 2014)). As a fusion of Augmented Reality (AR) and Virtual Reality (VR), MR combines the contextual benefits of AR, which supports visual learning by overlaying information on real-world objects, with the immersive experience of VR, which simulates real-life environments ((Cabero-Almenara et al., 2020); (Ali et al., 2018)). This unique combination makes MR an effective tool for fostering deeper understanding and engagement in educational settings.

The integration of technology in learning is essential for fostering students' literacy and numeracy skills (Fatahillah et al., 2020). Establishing a strong literacy and numeracy environment from an early age significantly influences children's mastery of reading, counting, and mathematical reasoning (Manolitsis et al., 2013). Numeracy literacy refers to the ability to understand and use numbers, symbols, and basic mathematical concepts to solve real-life problems, analyze data, interpret information, and make informed decisions (Culture, 2017). Although numeracy is often equated with mathematics, many students find mathematics challenging due to its abstract nature (Agustina & Martha Rusmana, 2019). (Ekowati et al., 2019) describe numeracy literacy as the ability to apply logical reasoning in mathematical contexts. To enhance this skill, learning media must go beyond traditional audio-visual methods. Engaging, interactive tools can make learning enjoyable and reduce boredom (Putri, 2022).

One promising tool for developing numeracy literacy is a Mixed Reality (MR)-enhanced digital book, which merges real and virtual environments by combining Augmented Reality (AR) and Virtual Reality (VR). This hybrid approach offers an immersive and interactive learning experience that helps students visualize mathematical concepts more clearly.

Discussions with the Semarang City Subject Teacher Conference highlighted that Class VII algebra materials require concrete contextualization due to their abstract nature. Existing teaching materials lack real-world visualization, creating a gap in students' understanding. Therefore, this study aims to design and develop a Mixed Reality-Based Digital Book for Class VII Algebra, test its validity, and evaluate its readability to improve students' numeracy literacy skills.

This study followed the research and development (R&D) model established by Borg and Gall, as described by Sugiyono (2016). The model outlines ten systematic development steps: (1) Research and Information Collection, (2) Planning, (3) Developing a Preliminary Product, (4) Conducting Preliminary Field Testing, (5) Revising the Main Product, (6) Conducting Main Field Testing, (7) Revising the Operational Product, (8) Conducting Operational Field Testing, (9) Final Product Revision, and (10) Dissemination. For the purpose of this research, the focus was limited to the third step, Developing the Preliminary Product, specifically through expert validation and readability testing.

The development process began with the Research & Information Collection stage, which included field studies and literature reviews. During the field study, researchers identified key challenges and gathered data necessary for designing a mixed reality-based digital algebra book. The literature review involved examining prior research findings as references for potential solutions and exploring relevant theories and concepts related to the research problem. The Planning stage involved setting clear research objectives, defining goals for each development phase, and determining the expertise required to address identified challenges effectively. The Preliminary Product Development stage included designing the first draft of the mixed reality-based digital algebra book (Draft 1), conducting expert validation, and revising the draft based on the feedback received. This iterative process ensured the product met both educational and technical standards. The overall development process is illustrated in Figure 1.

The data collection procedure for this study involved expert validation of the mixed reality-based digital algebra book design. The validation process was conducted using the expert judgment method combined with focus group discussions (FGD). The validation panel consisted of five mathematics teachers and two mathematics education lecturers, ensuring a diverse range of expertise. To gather validation data, researchers used customized validation sheets, readability assessment forms, and discussion note sheets designed specifically to evaluate the functionality, content accuracy, and usability of the digital book. This comprehensive approach ensured that both educational content and technological aspects of the digital book met the required standards.

In this study, a mixed reality-based digital algebra book was developed following the Borg and Gall model of development research, with each stage carefully adapted to align with the study’s specific objectives.

Based on the results of problem identification and data collection, it became evident that existing teaching materials for algebra lack technological integration that facilitates easier student learning. Current materials neither represent real-world objects nor relate to students' daily lives. To address this gap, this research developed teaching materials using E-modules packaged as digital books, which can be accessed via laptops and mobile phones, ensuring availability anytime and anywhere (Li et al., 2011). According to(Ran & Jinglu, 2020-10), digital books provide learners with greater flexibility and play a crucial role in constructing learning resources. (Fang et al., 2011) also highlights that digital books digitize traditional printed materials into accessible digital files, viewable on various devices such as mobile phones and computers. Integrating technology into learning must align with literacy and numeracy development, making the educational experience more meaningful. The use of digital books during the learning process has been found to enhance students' higher-order thinking and literacy skills (Siregar et al., 2021). while also fostering reading literacy (Febriana & Nugroho, 2023). The (O.E.C.D., 2020) defines literacy and numeracy as the ability of learners to formulate, apply, and interpret mathematics in various real-life contexts, which are critical skills supporting academic achievement and lifelong learning (, 2024). To bridge the gap between real-world environments and digital learning, Mixed Reality (MR) emerges as a promising technology. MR combines elements of virtual reality (VR), augmented reality (AR), and the real world to create immersive learning experiences (Carre et al., 2022). This technology blends real and virtual worlds to contextualize user perception, enhancing the learning process (Leonard & Fitzgerald, 2018). In the educational field, MR has demonstrated significant potential by facilitating better understanding through the integration of realistic and interactive learning environments (Kerdvibulvech, 2022); (Marın & Vega, 2022)). Guided by these insights, researchers designed a Mixed Reality-based digital book for algebra instruction, with a particular emphasis on improving literacy and numeracy skills. This digital book visualizes algebraic concepts in real-life contexts through a customized virtual environment, making learning more engaging and accessible to students.

The validation results confirmed that the mixed reality-based algebra digital book designed to enhance students' literacy and numeracy skills met the required validity criteria. Validators emphasized that the digital book is engaging, easy to understand, and effective in fostering critical thinking. The presentation style aligns well with the developmental characteristics of grade 7 students, incorporating numeracy literacy activities and recognizing various emotional and character aspects. As noted by Ernia and Mahmudah (2023), digital books can effectively train students' numeracy literacy. Validators also highlighted that this digital book simplifies lesson planning and instructional delivery for teachers, supporting improved teaching practices. According to Sandy et al. (2022), using digital books in teaching can enhance students' mathematical communication skills while assisting teachers in delivering content effectively. The validators also noted that the book’s content is logically structured, with clearly presented topics and terminology appropriate for the students' knowledge levels. This digital book aligns well with introducing and reinforcing numeracy literacy (Hamiedah et al., 2023). Its innovative and interactive features make it an effective tool for classroom learning, enhancing both student engagement and performance (Nugroho & Purwati, 2015). Additionally, the interactive design enables students to learn independently and strengthens their problem-solving abilities (Utami et al., 2018).

The readability test results involving teachers, lecturers, and students confirmed that the digital book is feasible and easy to use. The content, language, and instructions are clear and easy to follow, while the cover design and internal layout are visually appealing. The real-life examples, practice exercises, and animated illustrations in the digital book help simplify complex concepts. Each chapter includes virtual reality-enhanced content illustrating key problems, which improves understanding. As (Devetak & Vogrinc, 2013) argue, the effectiveness of teaching materials depends on the quality of their language, as text forms the foundation of educational content. Factors such as text structure, vocabulary difficulty, coherence, and syntax play significant roles in determining readability (Maulita, 2023).

Overall, the mixed reality-based digital book has proven to be an accessible and effective learning tool, enabling students to learn independently and gain a better understanding of algebra through contextualized, interactive content. Additionally, its design incorporates feedback from the Semarang City Subject Teacher Conference (FGD) to ensure alignment with the grade 7 algebra curriculum, further supporting its practical application in real educational settings

This study developed a mixed reality-based algebra digital book following the Borg and Gall model. The validation and readability test results confirmed that the digital book is valid, suitable for use, and effectively supports the improvement of students’ literacy and numeracy skills in algebra. Feedback from validators was carefully considered and integrated into the final design, enhancing the quality and usability of the digital book.

The digital book creates an immersive learning environment closely related to students’ real-world experiences through mixed reality technology, making abstract algebraic concepts more accessible and engaging. Its design aligns with the specific learning needs of both teachers and students, offering a practical and interactive learning tool.

This research, however, is limited to the validation and readability test phases. Future studies should extend the work to the implementation stage, evaluating its impact on learning outcomes in classroom settings and exploring its potential for broader educational applications.

The researcher would like to thank the Ministry of Education, Culture, Research and Technology for providing support in this research; the Higher Education Service Institution Region VI and the Institute for Research and Community Service of PGRI Semarang University for assisting the implementation of this research; and MGMP Mathematics Semarang City Central Java as a partner in this research so that the data needed to answer the research objectives are obtained.